Spinneret plate



April 11, 1967 R. Y. HAYS SPINNERET PLATE Filed July 1;, 1 965 United States Patent 3,313,000 SPINNERET PLATE Richard Young Hays, Kinston, N.C., assignor to E. I. du Pont de Nernours and Company, Wilmington, Del., a corporation of Delaware Filed July 13, 1965, Ser. No. 471,527 4 Claims. (Cl. 18-8) This invention relates generally to the melt spinning of hollow filaments from synthetic polymers and, more particularly, to a spinneret nozzle configuration which facilitates the production of improved hollow filaments.

Synthetic filaments are spun by forcing a molten material such as nylon, under pressure, through a plurality of extrusion orifices formed in a spinneret or spinneret plate from which the material issues in the form of continuous filaments which solidify on cooling. The orifices are generally of circular form and the resulting filaments are of solid circular form. However, there is a growing demand for filaments of other configurations. It is known, for example, that odd-shaped cross sections impart desirable fabric aesthetics. Hollow filaments are also being used for improved textile properties.

Initially, hollow filaments were spun by forcing melts through a spinneret nozzle which contained a small tube through which gas was supplied to the filament center. Such arrangements are relatively complicated. In recent years, it has been found possible to spin through segmented orifices and have the sections of polymer coalesce in the form of a hollow filament below the spinneret. Although entirely satisfactory for use in textile applications, such filaments perform inadequately in other applications, for example, when used to meter fluids in testing devices or as capillary flow tubes in permeation separation cells. These and analogous usages require hollow filaments of minimum wall thickness and maximum wall strength, high resistance to rupture and an absence of localized weak spots.

The general objective of this invention is to provide for production of hollow filaments suitable for use as capillary flow tubes. A more particular objective is the provision of a spinneret nozzle configuration which facilitates production of hollow filaments having very small diameters and a high degree of uniformity.

These and other objectives are achieved with a spinneret plate having specially configured nozzles. Each nozzle starts in an entrance hole and has a discharge capillary opening into the other face of the plate. The capillary is defined by a substantially symmetrical pattern of arcuate slots interrupted by webs. Each slot progressively increases in width from a minimum at its mid-point to maxima at the adjacent webs. Except for one which extends to the discharge surface of the plate, all webs are recessed.

In the drawings,

FIGURE 1 is a fragmentary, bottom view of a spinneret plate showing the exit orifice of one spinning nozzle; and

FIG. 2 is a sectional view taken on irregular line IIII in FIG. 1, after returning the plate to its normal or upright position.

Only one of the plurality of spinning nozzles usually provided in a spinneret plate has been shown. It starts in an entrance hole 12 and discharges through a capillary 14 which presents an exit orifice in the bottom face of plate 10. Capillary 14 is defined by a substantially symmetrical pattern of arcuate, end-to-end slots 16, 17, 18 which are interrupted by webs 20, 21, 22 but otherwise surround a solid center portion 24. Thus, center portion 24 remains integrally attached to plate 10 by the webs.

3,3 13 ,00 0 Patented Apr. 11, 1967 ice Since web 22 extends to the face of plate 10, it has been referred to herein as a surface web. The bottom face of plate 10 is recessed at the locations of webs 20, 21. Each of slots 16, 17, 18 progressively increases in width from a mid-point to its ends. For example, slot 17 increases in width from a minimum at mid-point 17a to a maximum at end locations 17b adjacent webs 21, 22.

The illustrated width variations have been achieved by fabricating the inner wall of each capillary slot on a smaller radius than that of the outer wall. In addition to the width variations, each of the arcuate slots 16, 17, 18 is bowed outwardly from the pattern center, i.e., both of the above radii are shorter than the distance to the pattern center.

In operation, hollow filaments of increased wall strength are spun by supplying molten polymer to each entrance hole 12 under sufiicient pressure to extrude it out of the capillary 14. Due to the recessed webs 20, 21, polymer will be kept apart until it nears the exit of capillary 14 and flows back together, forming a longitudinal seam. The surface web 22 prevents the molten polymer tfrom flowing back together until after it leaves the bottom face of plate 10. However, shortly after leaving the spinneret, edges of the extrudates are coalesced together. Entry of air before this final coalescence prevents collapse of the resulting hollow filament. Since the orifices presented by slots 16, 17, 18 are wider adjacent the web portions, more polymer is extruded and the wall thickness is greater at the seams. The resulting increases in the areas of coalescence or adhesion produce stronger welds. In this manner, the resistance to bursting strength is increased substantially without increasing wall thickness through the circumference and, therefore, without lessening the rate at which one component of a fluid passing through the hollow filament under pressure can be separated out by activated diffusion (U.S. Patent 3,019,853).

Various modifications and design variations may occur to those skilled in the art without departure from the spirit of my invention which accordingly is intended to be limited only by the scope of the following claims.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

1. A spinneret plate provided with at least one nozzle having a discharge capillary opening into one face of the plate, said capillary being defined by a substantially symmetrical pattern of arcuate, end-to-end slots interrupted by webs, each slot progressively increasing in width from a minimum at its mid-point to a maximum adjacent its ends.

2. The spinneret plate of claim 1 wherein each slot is bowed with its mid-point spaced farther from the pattern center than its ends.

3. The spinneret plate of claim 2 wherein said one face of the plate is recessed at the location of at least one of said webs and wherein another of said webs extends to and is a part of said one face of the plate.

4. A spinneret plate provided with at least one nozzle having a discharge capillary opening into one surface of the plate, said capillary being defined by a complex pattern of arcuate slots separated by webs, one of said webs extending to and forming a part of said surface, said surface being recessed at the location of the remaining webs.

References Cited by the Examiner UNITED STATES PATENTS WILLIAM J. STEPHENSON, Primary Examiner. 

1. A SPINNERET PLATE PROVIDED WITH AT LEAST ONE NOZZLE HAVING A DISCHARGE CAPILLARY OPENING INTO ONE FACE OF THE PLATE, SAID CAPILLARY BEING DEFINED BY A SUBSTANTIALLY SYMMETRICAL PATTERN OF ARCUATE, END-TO-END SLOTS INTERRUPTED BY WEBS, EACH SLOT PROGRESSIVELY INCREASING IN WIDTH FROM A MINIMUM AT ITS MID-POINT TO A MAXIMUM ADJACENT ITS ENDS. 